Abstract:

A low dielectric constant material having an excellent water resistance
obtained by heat-treating a borazine compound of the formula (1-2):
##STR00001##
or an inorganic or organic compound having a group derived from the
borazine compound (1-2) to undergo a condensation reaction, thereby
producing an oligomer or polymer, wherein R1 to R6 are
independently a hydrogen atom, an alkyl group having 1 to 20 carbon
atoms, an aryl group, a substituted aryl group, an alkenyl group, an
amino group, an alkylamino group, an alkoxyl group, a thioalkoxyl group,
a carbonyl group, a silyl group, an alkylsilyl group, a phosphino group,
an alkylphosphino group, or a group of the formula:
Si(OR7)(OR8)(OR9), and at least one of R1 to R6
is not hydrogen atom.

Claims:

1-14. (canceled)

15. Source material for preparing a low dielectric constant material
comprising a borazine skeleton structure having formula (1-1):
##STR00019## wherein at least one of R1 to R6 is a bond to an
oligomer or polymer comprising a repeating borazine skeleton structure
and R1 to R6, other than said bond, are, independently, a
hydrogen atom or an alkyl group having 1 to 2 carbon atoms.

16. The source material of claim 15, wherein R1, R3, and R5
are not hydrogen.

17. Source material for preparing a low dielectric constant material
comprising a borazine skeleton structure having formula (1-1):
##STR00020## wherein at least one of R1 to R6 is a bond to an
oligomer or polymer comprising a repeating borazine skeleton structure
and R1 to R6, other than said bond, are, independently, a
hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group,
a substituted aryl group, an alkenyl group, an alkylamino group, an
alkoxyl group, a thioalkoxyl group, SiH3, or an alkylsilyl group.

Description:

BACKGROUND OF THE INVENTION

[0001]The present invention relates to a material having a low dielectric
constant (low k material) useful as an insulating film used for
interlayer insulation of semiconductor elements, as a barrier metal layer
or an etch stopper layer, or as a substrate for electric circuit parts,
and also relates to an insulating film comprising this material and a
semiconductor device having the insulating film.

[0002]Demands for high integration and high speed of semiconductor devices
are increasing more and more. In order to meet these demands, there have
been made a study on conductive layer materials having a lower electric
resistance than conventional aluminum alloy, namely a study on wiring
materials, and a study on insulating layer materials having a lower
dielectric constant than conventional silicon oxide. In particular, these
materials are needed in wiring of semiconductor devices if the structural
minimum dimension of the semiconductor devices becomes smaller than about
0.18 μm, as known, for example, from "Recent Development in Cu Wiring
Technology" edited by S. Shinmiyahara, N. Awaya, K. Ueno and N. Misawa
published by Realize Company, Japan in 1998.

[0003]FIG. 5 is a section view showing a two layer copper wiring structure
in a semiconductor device disclosed in the above publication. In the
figure, numeral 1 is a silicon substrate, and numeral 2 is a first
insulating layer having trench 3 corresponding to a first wiring pattern.
The first insulating layer 2 is made of a silicon oxide film having a
dielectric constant of 4.2 or a fluorine-containing silicon oxide film
having a dielectric constant of 3.2 to 3.5. Further, studies have been
made on applicability, as alternates, of materials having a lower
dielectric constant than 2.8 such as silicon-based inorganic polymer
materials, organic polymer materials, amorphous fluorine-containing
carbon films and porous silicon oxide films. The bottom and the side
faces of trench 3 are covered with first conductive film 4 having a
diffusion preventive function as a barrier metal. As the first conductive
film 4 is used titanium nitride (TiN), tantalum nitride (TaN), tungsten
nitride (WN), or a trinary barrier metal comprising each of these
nitrides and silicon. First copper conductive layer 5 is formed to fill
the trench 3 covered with the first conductive film 4. Numeral 6 is a
first insulating film having a diffusion preventive function against
copper, which is made of silicon nitride. Numeral 7 is a second
insulating layer, which is made of a material similar to that of the
first insulating layer 2. A hole 8 is formed in the first insulating film
6 and the second insulating layer 7 therethrough, and the bottom and side
surfaces of the hole 8 are covered with a second conductive film 9 having
a diffusion preventive function and contacting the first copper
conductive layer 5. The hole 8 which is covered with the second
conductive film 9 is filled with a second copper conductive layer 10. A
trench 12 corresponding to a second wiring pattern is also formed in the
second insulating layer 7, and the inner surfaces of trench 12 are
covered with third conductive film 11 having a diffusion preventive
function. The trench 12 which is covered with the third conductive film
11 is filled with a third copper conductive layer 13. The second and
third conductive films 9 and 11 are made of a material similar to that of
the first conductive film 4. The upper surface of the third copper
conductive layer 13 is covered with a second insulating film 14 made of
silicon nitride having a diffusion preventive function against copper.
The first and third copper conductive layers 5 and 13 constitute wiring
in the lower layer and wiring in the upper layer respectively, and the
second copper conductive layer 10 electrically connects these wirings in
the upper and lower layers therebetween. While the wiring of two layer
structure is shown in FIG. 4, this structure may be repeatedly stacked to
form a multi-layer structure.

[0004]The wiring structure shown in FIG. 5 is formed through a so-called
Damascene process, which will be described below.

[0005]Trench 3 corresponding to a wiring pattern is formed in first
insulating layer 2, and first conductive film 4 which serves as a barrier
metal, is formed on the inner surface of the trench 3. A copper film is
is then formed on the first insulating layer 2 to fill the trench 3.
Unnecessary barrier metal and copper films formed on portions other than
the trench 3 are removed by CMP (chemical mechanical polishing) to leave
the barrier metal and copper only in the trench 3 to form first copper
conductive layer 5. In such a manner, the copper wiring in the lower
layer is formed in the trench 3 with the bottom and side surfaces thereof
covered with the first conductive film 4. Then, silicon nitride film 6
and second insulating layer 7 are sequentially stacked on the first
insulating layer 2. Trench 12 having a pattern corresponding to the
second wiring and hole 8 extending to the first copper conductive layer 5
are formed in the silicon nitride film 6 and the second insulating layer
7 therethrough. Second and third conductive films 9 and 11 are formed as
the barrier metal on the surfaces of the trench 12 and the hole 8. The
trench 12 and the hole 8 are then filled with copper by copper film
forming, followed by removal of unnecessary copper and barrier metal on
the second insulating layer 7 using CMP to thereby form the wiring in the
upper layer. Thereafter, second insulating film 14 is formed.

[0006]In case that a polymeric material or a porous silicon oxide, which
have a lower dielectric constant than silicon oxide and
fluorine-containing silicon oxide, is used as a material for the first or
second insulating layer or the first or second insulating film of
semiconductor devices having the above wiring structure, a problem arises
about deterioration in reliability of wiring and device, since these
materials have a lower thermal conductivity as compared with
conventionally used silicon oxide and heat generation in a wiring may
cause temperature rise of semiconductor devices.

[0007]FIG. 6 is a section view showing a wiring structure in a
semiconductor device disclosed in W. Y. Shih, M. C. Chang, R. H. Havemann
and J. Levine, Symposium on VLSI Technology Digest, pages 83-84, 1997,
wherein two kinds of insulative materials are used in the above-mentioned
first and second insulating layers respectively in order to solve the
problem associated with poor thermal conductivity.

[0008]That is to say, a material having a low dielectric constant such as
a polymeric material is used as a material of insulating layers 15 and 16
in which wiring is formed by each of first copper conductive layer 5 and
third copper conductive layer 13. On the other hand, silicon oxide which
has a good thermal conductivity and has been conventionally used as an
insulating material of a wiring-forming layer, is used as a material of
insulating layer 18 in which hole 8 is formed and as a material of
insulating layer 17 disposed between first copper wiring 5 and substrate
1, thereby suppressing deterioration in thermal conductivity as a whole.
Numerals 4, 9 and 11 denote first, second and third conductive films
respectively which are formed as a barrier metal. Numeral 10 is a second
copper conductive layer filled in the hole 8. Numeral 12 is a trench, and
numeral 14 is a second insulating film.

[0009]In the former publication, it is described that owing to scale down
of pattern size associated with high integration of integrated circuits
in semiconductor devices and owing to increase in wiring length resulting
from increase in chip area, propagation delay of signals on wiring is
growing to a major cause hindering advent of high speed devices. Solution
of such a problem would require reduction in wiring resistance and use of
insulating films having low dielectric constant for reduction in
electrostatic capacitance between wirings, namely reduction in wiring
capacitance. As a wiring material for this purpose, copper is beginning
to be used in place of aluminum alloy used conventionally. On the other
hand, as an interlayer dielectric for this purpose, a fluorine-containing
silicon oxide film having a dielectric constant of 3.2 to 3.5, namely
SiOF, is also beginning to be used in place of silicon oxide having a
dielectric constant of 4.2.

[0010]However, in case of forming an interlayer insulating film from SiOF,
its dielectric constant is from about 3.2 to about 3.5 and, therefore,
the reduction in capacity between wirings and the prevention of
propagation delay of signals on wiring are not sufficiently achieved,
although the dielectric constant of interlayer insulating film becomes
lower than conventional one.

[0011]With respect to interlayer insulating films formed from organic
compounds, dielectric constant of 2.7 is achieved by a film of a
polyimide into which fluorine atom is introduced or by an aryl ether
polymer, but they are still unsatisfactory for use as an interlayer
dielectric. A deposition film of parylene can achieve a dielectric
constant of 2.4, but its thermal resistance is at most about
200-300° C. and, therefore, processes for the production of
semiconductor elements are restricted.

[0012]Also, a porous SiO2 film having a dielectric constant of 2.0 to
2.5 is reported, but it is poor in mechanical strength (resistance to CMP
process) due to high porosity and has a problem that the pore size is not
uniform.

[0013]Further, these polymeric materials and porous SiO2 film have an
inferior thermal conductivity as compared to conventional SiO2
interlayer dielectrics and accordingly may cause a problem of
deterioration in wiring life (electromigration) due to rise in
temperature of wiring.

[0014]Use of copper as a wiring material requires covering the surface of
copper wiring with a diffusion preventive film, since copper easily
diffuses into insulating layers under application of an electric field.
Therefore, in general, the lower and side surfaces of a copper wiring are
covered with a conductive barrier metal, while the top surface thereof is
covered with a silicon nitride insulating film. The dielectric constant
of the silicon nitride film is about 7 and the resistance of the barrier
metal is much higher than that of copper. Thus, the resistance value of
the wiring as a whole increases to result in restriction on speeding up
in operation of semiconductor devices.

[0015]The same problem is also encountered when a low dielectric constant
material is used as an insulating film. In case of using low dielectric
constant insulating films, conventional silicon oxide which has a good
thermal conductivity is used as a material of a layer provided with a
hole for connecting the upper wiring with the lower wiring in order to
avoid reduction in reliability. Since the use of this silicon oxide layer
further increases wiring capacitance, a problem arises that the
propagation delay of signal is caused by increase in wiring capacitance,
thus resulting in restriction on speeding up of semiconductor devices.

[0016]As a material having a low dielectric constant and a thermal
resistance which would solve the problems as mentioned above,
JP-A-2000-340689 and JP-A-2001-15496 propose low dielectric constant
materials that have a borazine skeleton-based molecule in an inorganic or
organic material molecule. However, the proposed low dielectric constant
materials have the problem that since they are hydrolyzable, the water
resistance is poor.

[0017]It is an object of the present invention to provide a low dielectric
constant material free from the problems as mentioned above, particularly
a low dielectric constant material having an excellent water resistance
as well as a low dielectric constant and a high thermal resistance.

[0018]A further object of the present invention is to provide a low
dielectric constant insulating film having an excellent water resistance
suitable for use in semiconductor devices.

[0019]A still further object of the present invention is to provide a
process for preparing a low dielectric constant material having an
excellent water resistance as well as a low dielectric constant and a
high thermal resistance.

[0020]Another object of the present invention is to provide a
semiconductor device capable of operating in high speed and having a high
reliability.

[0021]These and other objects of the present invention will become
apparent from the description hereinafter.

SUMMARY OF THE INVENTION

[0022]In accordance with the first aspect of the present invention, there
is provided a process for preparing a low dielectric constant material
comprising the step of heat-treating an inorganic or organic compound
containing in its molecule a borazine skeleton structure of the formula
(1-1):

##STR00002##

wherein at least one of R1 to R6 is a bond which binds said
borazine skeleton structure to the molecule of said inorganic or organic
compound, and R1 to R6 other than said bond are independently a
hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group,
a substituted aryl group, an alkenyl group, an amino group, an alkylamino
group, an alkoxyl group, a thioalkoxyl group, a carbonyl group, a silyl
group, an alkylsilyl group, a phosphino group, an alkylphosphino group or
a group of the formula: Si(OR7)(OR8)(OR9) in which R7
to R9 are independently a hydrogen atom, an alkyl group having 1 to
20 carbon atoms, an aryl group, a substituted aryl group, an alkenyl
group, an amino group, an alkylamino group, an alkoxyl group, a
thioalkoxyl group, a carbonyl group, a silyl group, an alkylsilyl group,
a phosphino group or an alkylphosphino group, provided that at least one
of R1 to R6 other than said bond is not a hydrogen atom.

[0023]In accordance with the second aspect of the present invention, there
is provided a process for preparing a low dielectric constant material
comprising the step of heat-treating a borazine skeleton-containing
compound of the formula (1-2):

##STR00003##

wherein R1 to R6 are independently a hydrogen atom, an alkyl
group having 1 to 20 carbon atoms, an aryl group, a substituted aryl
group, an alkenyl group, an amino group, an alkylamino group, an alkoxyl
group, a thioalkoxyl group, a carbonyl group, a silyl group, an
alkylsilyl group, a phosphino group, an alkylphosphino group, or a group
of the formula: Si(OR7)(OR8)(OR9) in which R7 to
R9 are independently a hydrogen atom, an alkyl group having 1 to 20
carbon atoms, an aryl group, a substituted aryl group, an alkenyl group,
an amino group, an alkylamino group, an alkoxyl group, a thioalkoxyl
group, a carbonyl group, a silyl group, an alkylsilyl group, a phosphino
group or an alkylphosphino group, and at least one of R1 to R6
is not a hydrogen atom.

[0024]Low dielectric constant materials having an excellent water
resistance as well as a low dielectric constant and a high thermal
resistance can be obtained by the above first and second processes.

[0025]Thus, the present invention provides a low dielectric constant
material (material I) comprising a polymeric or oligomeric, inorganic or
organic material having in its molecule a borazine skeleton structure
represented by any of the formulas (2) to (4):

##STR00004##

wherein R1 to R4 are independently a hydrogen atom, an alkyl
group having 1 to 20 carbon atoms, an aryl group, a substituted aryl
group, an alkenyl group, an amino group, an alkylamino group, an alkoxyl
group, a thioalkoxyl group, a carbonyl group, a silyl group, an
alkylsilyl group, a phosphino group, an alkylphosphino group, or a group
of the formula: Si(OR7)(OR8)(OR9) in which R7 to
R9 are independently a hydrogen atom, an alkyl group having 1 to 20
carbon atoms, an aryl group, a substituted aryl group, an alkenyl group,
an amino group, an alkylamino group, an alkoxyl group, a thioalkoxyl
group, a carbonyl group, a silyl group, an alkylsilyl groups a phosphino
group or an alkylphosphino group, provided that at least one of R1
to R4 is not a hydrogen atom.

[0026]The present invention also provides a low dielectric constant
material (material II) obtained by condensation of the compound (1-2),
that is, a low dielectric constant material having a borazine
skeleton-based structure formed by bonding a first borazine skeleton
structure represented by any one of the formulas (2) to (4) described
below with a second borazine skeleton structure represented by any one of
the formulas (2) to (4) with elimination of hydrogen atoms from each of
the first and second borazine skeleton structure to form a third borazine
skeleton structure:

##STR00005##

wherein R1 to R4 are independently a hydrogen atom, an alkyl
group having 1 to 20 carbon atoms, an aryl group, a substituted aryl
group, an alkenyl group, an amino group, an alkylamino group, an alkoxyl
group, a thioalkoxyl group, a carbonyl group, a silyl group, an
alkylsilyl group, a phosphino group, an alkylphosphino group, or a group
of the formula: Si(OR7)(OR8)(OR9) in which R7 to
R9 are independently a hydrogen atom, an alkyl group having 1 to 20
carbon atoms, an aryl group, a substituted aryl group, an alkenyl group,
an amino group, an alkylamino group, an alkoxyl group, a thioalkoxyl
group, a carbonyl group, a silyl group, an alkylsilyl group, a phosphino
group or an alkylphosphino group, provided that at least one of R1
to R4 is not a hydrogen atom.

[0027]The low dielectric constant materials of the present invention are
useful as an insulating film for use in semiconductor devices, and
semiconductor devices having excellent properties are obtained by the use
thereof.

[0028]Thus, in accordance with another aspect of the present invention,
there is provided an insulating film comprising the above-mentioned low
dielectric constant material I or II.

[0029]In accordance with still another aspect of the present invention,
there is provided a semiconductor device including such insulating film.
The semiconductor devices of the present invention are operable at high
speed.

[0030]In a first embodiment of the semiconductor devices according to the
present invention, the semiconductor device comprises a semiconductor
substrate, a first insulating layer having a first trench and being
formed on the surface of said semiconductor substrate, a first copper
conductive layer formed so as to fill said first trench, a second
insulating layer having a hole communicating with said first copper
conductive layer, a second copper conductive layer filled in said hole so
as to contact with said first copper conductive layer, a third insulating
layer formed on said second insulating layer and having a second trench
communicating with said second copper conductive layer, and a third
copper conductive layer contacting said second copper conductive layer
and being formed so as to fill said second trench formed in said third
insulating layer, wherein at least one of said first, second and third
insulating layers is made of an insulating material comprising the
above-mentioned low dielectric constant material I or II.

[0031]In a second embodiment of the semiconductor devices according to the
present invention, the semiconductor device comprises a semiconductor
substrate, a first insulating layer having a first trench and formed on
the surface of said semiconductor substrate, a first copper conductive
layer formed so as to fill said first trench, an insulating film which
has a first hole communicating with said first copper conductive layer
and which covers said first copper conductive layer and said first
insulating layer, a second insulating layer having a second hole
communicating with said first hole and having a second trench
communicating with said second hole, a second copper conductive layer
filling said first and second holes so as to contact with said first
copper conductive layer, and a third copper conductive layer contacting
with said second copper conductive layer and being formed so as to fill
said second trench formed in said second insulating layer, wherein said
insulating film is made of an insulating material comprising the
above-mentioned low dielectric constant material I or II.

[0032]In the above embodiments, from the viewpoints that the production of
semiconductor devices is easy and the reliability of the devices is high,
it is preferable that the low dielectric constant material I or II in the
insulating material is amorphous. Also, from the viewpoints of excellent
mechanical strength and high heat resistance, it is preferable that the
low dielectric constant material I or II in the insulating material is a
mixture of a microcrystalline material and an amorphous material.

[0033]In the semiconductor device according to the first embodiment, from
the viewpoint that the thermal conductivity is excellent and accordingly
the reliability is improved, it is preferable that at least one of the
first, second and third insulating layers is made of silicone oxide.
Also, from the viewpoint that wiring having a good shape is obtained and
accordingly the reliability is improved, it is preferable that at least
one of the first, second and third insulating layers is made of an aryl
ether polymer.

BRIEF DESCRIPTION OF DRAWINGS

[0034]FIG. 1 is a sectional view showing a wiring structure of a
semiconductor device according to an embodiment of the present invention;

[0035]FIG. 2 is a sectional view showing a wiring structure of a
semiconductor device according to an embodiment of the present invention;

[0036]FIG. 3 is a sectional view showing a wiring structure of a
semiconductor device according to an embodiment of the present invention;

[0037]FIG. 4 is a sectional view showing a wiring structure of a
semiconductor device according to an embodiment of the present invention;

[0038]FIG. 5 is a sectional view showing a wiring structure of a
conventional semiconductor device; and

[0039]FIG. 6 is a sectional view showing a wiring structure of a
conventional semiconductor device.

DETAILED DESCRIPTION

[0040]The low dielectric constant materials of the present invention are
prepared by subjecting a borazine derivative as a starting material,
i.e., an inorganic or organic compound containing a borazine skeleton
structure of the formula (1-1) in its molecule or a substituted borazine
(1-2), to a condensation reaction to produce an oligomer or polymer
containing the borazine skeleton structure.

[0041]The preparation of the low dielectric constant materials is carried
out, for example, according to the procedures as described in Yoshiharu
Kimura, Senni-to-Kogyo (Fiber and Industry), Vol. 52, No. 8, 341-346
(1996); Paine & Sneddon, Recent Developments in Borazine-Based Polymers,
"Inorganic and Organometallic Polymers", American Chemical Society,
358-374 (1994); and Fazen et al., Chem. Mater., Vol. 7, p 1942 (1995).
That is, the low dielectric constant materials can be obtained by heating
a borazine derivative as the starting material to undergo a condensation
reaction, or by firstly synthesizing a prepolymer in such a manner and
then polymerizing it. In general, the condensation reaction is carried
out by heating the starting material in an organic solvent at a
temperature of 50 to 400° C., preferably 70 to 180° C. for
1 to 240 hours, preferably in an inert gas atmosphere such as argon.

[0042]In the preparation of low dielectric constant materials is used an
organic solvent which can homogeniously disperse or dissolve borazine,
borazine derivatives as mentioned above or borazine-based prepolymers,
e.g., an alcohol such as methanol, ethanol, propanol or butanol, acetone,
benzene, toluene, xylene, glyme and others.

[0043]An example of the substituted borazine (1-2) is
B-triethylaminoborazine. B-triethylaminoborazine can be prepared, for
example, by reacting B-trichloroborazine with ethylamine in toluene at an
elevated temperature, e.g., 70° C., for several hours, e.g., 4
hours, and removing ethylamine hydrochloride and the solvent.

[0044]In the inorganic or organic compound containing a borazine skeleton
structure of the formula (1-1) in its molecule, the inorganic compound to
which the substituted borazine (1-2) is bound includes, for instance,
silicate, silazane, silsequioxane, siloxane, silane and the like. The
organic compound to which the substituted borazine (1-2) is bound
includes, for instance, poly(aryl ether), parylene, polyphenylene,
polyphenylenevinylene, polybenzocyclobutene, polyimide, polyester,
polystyrene, polymethylstyrene, polymethyl acrylate, polymethyl
methacrylate, polycarbonate, adamantane, norbornene, and the like.

[0045]The low dielectric constant materials of the present invention can
also be obtained by a chemical vapor deposition method, as described
after, using a boron source, a nitrogen source and a carbon or the like
source such as methane, a chemical vapor deposition method using a
substituted borazine such as methylborazine or ethylborazine, or by
methods as disclosed in C. K. Narula et al., J. Am. Chem. Soc., Vol. 109,
p 5556 (1987) and Y. Kimura et al., Composites Science and Technology,
Vol. 51, p 173 (1994).

[0046]The low dielectric constant materials of the present invention
prepared from the inorganic or organic compound containing in its
molecule the borazine skeleton structure shown by the formula (1-1) are
inorganic or organic oligomers or polymers containing a borazine skeleton
structure shown by the formula (2), (3) or (4) in the molecule thereof.
These oligomers and polymers have a lower dielectric constant than
silicon oxide and fluorine-containing silicon oxide, and an excellent
water resistance. They are composed of, as a main component, boron
nitride which has a copper diffusion preventing function and accordingly
can prevent diffusion of copper.

[0047]Examples of the borazine skeleton structures included in the
oligomers or polymers are those having the formulas (5) to (116) shown
below.

[0048]The low dielectric constant materials according to another
embodiment of the present invention are condensates of the substituted
borazine (1-2), in other words, compounds having a third borazine
skeleton-based structure formed by bonding a first borazine skeleton
structure represented by any one of the formulas (2) to (4) with a second
borazine skeleton structure represented by any one of the formulas (2) to
(4) with elimination of hydrogen atoms from each of the molecules of a
substituted borazine to form the third borazine skeleton structure.
Examples of the condensates are, for instance, compounds having borazine
skeletons structures shown by the above formulas (25) to (28).

[0049]The reason why the low dielectric constant material of the present
invention can achieve a low dielectric constant is considered that the
electronic polarization is decreased by an ionic electronic structure of
the borazine skeleton.

[0050]Also, a high heat resistance can be achieved by the low dielectric
constant materials of the present invention, since inorganic polymeric
materials which have of course a higher heat resistance than organic
polymeric materials are used.

[0051]Further, the reason why the low dielectric constant materials of the
present invention have a high water resistance is considered that if
R1 to R4 is substituents other than hydrogen atom in the
formulas (2) to (4), they firmly bond to boron atom or nitrogen atom in
the borazine skeleton and are prevented from reacting with water. Since a
hydrogen atom bonding to a boron atom or a nitrogen atom is easily
hydrolyzed, it is necessary that in the low dielectric constant material
of the present invention, at least one of R1 to R4 in the
formulas (2) to (4) is not a hydrogen atom, but a substituent. In
particular, since a hydrogen atom bonding to a boron atom causes a
hydrolysis reaction more easily as compared with that bonding to a
nitrogen atom, it is preferable that a substituent is bonded to a boron
atom.

[0052]As to the degree of substitution, preferred from the viewpoint of
water resistance, of hydrogen atoms on the borazine skeletons included in
a molecule which constitutes the low dielectric constant material,
assuming that the degree of substitution is 100% if all hydrogen atoms on
the borazine skeletons are substituted by a substitutent or substituents
shown in the formulas (2) to (4), water resistance equivalent to that for
a degree of substitution of 100% is obtained when 30 to 40% of all
hydrogen atoms are substituted by a substitutent or substituents shown in
the formulas (2) to (4), namely when the degree of substitution is 30 to
40%.

[0053]The dielectric constant can be further lowered by introducing
fluorine atom (F) into boron nitride. Thus, an insulation layer having a
lower dielectric constant can be obtained thereby.

[0054]The insulating films of the present invention are obtained by
forming the low dielectric constant materials of the present invention
into thin films. The insulating films of the present invention are
applicable as an interlayer insulating film of semiconductor devices,
whereby excellent semiconductor devices can be obtained.

[0055]In case of using the low dielectric constant materials in the form
of a film, for example, as an interlayer insulating film for
semiconductor devices, the film can be formed by coating a solution or
dispersion of the low dielectric constant material in a solvent. In that
case, the low dielectric constant material may be used in combination
with other materials such as other insulating materials which are used
preferably in an amount of at most 20% by weight based on the total
weight of the low dielectric constant material of the present invention
and other materials. Examples of the other materials are, for instance, a
known interlayer insulating material for semiconductor devices such as
silicate, silazane, silsequioxane, siloxane, silane, polyaryl ether,
parylene or polybenzocyclobutadiene, a general insulating material such
as adamantane, norbornene, polyimide, polyester, polystyrene,
polymethylstyrene, polymethyl acrylate, polymethyl methacrylate or
polycarbonate, an amine such as cyclohexylamine, aniline or ethylamine, a
surface active agent, and the like. The coating to a substrate can be
conducted by spray coating, dip coating, spin coating or other known
coating methods. The solvent or dispersing medium includes, for instance,
acetone, benzene, glyme, tetrahydrofuran, chloroform and other organic
solvents capable of dissolving or dispersing the low dielectric constant
materials. The concentration is preferably from 10 to 30% by weight.
Preferably, after drying the coated film, the dried film is further
heat-treated to cure the film at a temperature of 300 to 450° C.,
preferably 350 to 400° C. The thickness of the insulating film is
preferably from 0.3 to 0.8 μm.

[0056]In case of using the low dielectric constant materials as a film
such as an interlayer insulating film for semiconductor devices, thin
films can also be formed according to procedures as described for example
in S. V. Nguyen, T. Nguyen, H. Treichel and O, Spindler, J. Electrochem.
Soc., Vol. 141, No. 6, 1633-1638 (1994); W. F. Kane, S. A. Cohen, J. P.
Hummel and B. Luther, J. Electrochem. Soc., Vol. 144, No. 2, 658-663
(1997); and M. Maeda and T. Makino, Japanese Journal of Applied Physics,
Vol. 26, No. 5, 660-665 (1987). For example, the insulating film or layer
can be obtained by subjecting a mixture of diborane (B2H6),
ammonia (NH3) and methane or a mixture of borazine
(B3H3N6), nitrogen (N2) and methane as a raw material
a chemical vapor deposition method (CVD method), thereby causing a
condensation reaction.

[0057]In case that the low dielectric constant materials are used in the
form of a bulk body as a low dielectric constant substrate, the materials
are molded by casting into a mold and heat-treating the resulting molded
article. The low dielectric constant material to be cast may be used in
combination with other materials as mentioned above. The content of other
materials is at most 20% by weight.

[0058]The insulating films of the present invention applicable to various
electronic parts as an interlayer insulating film for semiconductor
devices, as a barrier metal layer or etch stopper layer, and as an IC
substrate.

[0059]Thus, the present invention provides semiconductor devices including
an insulating layer or film made of the low dielectric constant materials
of the present invention.

[0060]In an embodiment of the semiconductor devices according to the
present invention, a first insulating layer having a first copper
conductive layer disposed to form a lower wiring and a third insulating
layer having a third copper conductive layer disposed to form an upper
wiring are stacked on the surface of a semiconductor substrate through a
second insulating layer interposed therebetween and having a second
copper conductive layer communicating with both the first copper
conductive layer and the third copper conductive layer so as to
electrically connect the lower wiring with the upper wiring. In this
embodiment, at least one of the first, second and third insulating layers
is made of an insulating material containing the low dielectric constant
material of the present invention.

[0061]In another embodiment of the semiconductor devices according to the
present invention, a first insulating layer having a first copper
conductive layer disposed to form a lower wiring and a second insulating
layer having a third copper conductive layer disposed to form an upper
wiring and having a second copper conductive layer communicating with
both the first copper conductive layer and the third copper conductive
layer so as to electrically connect the lower wiring with the upper
wiring are stacked on the surface of a semiconductor substrate through an
insulating film interposed therebetween, the second copper conductive
layer also extending through the insulating film. In this embodiment, the
insulating film interposed between the first and second insulating layers
is made of an insulating material containing the low dielectric constant
material of the present invention.

[0062]Since the insulating layer or film made of an insulating material
containing the low dielectric constant material of the present invention
is used in the above semiconductor devices instead of conventional
built-up films of silicon oxide and silicon nitride, the wiring
capacitance can be reduced.

[0063]Also, since the insulating layer or film is made of an insulating
material containing the low dielectric constant material of the present
invention which has a copper diffusion preventing function, it is not
needed to use a barrier metal layer at connecting hole portions and,
therefore, a low resistant wiring can be obtained and it is possible to
operate the semiconductor devices at high speed.

[0064]In the above embodiments, the first, second and third conductive
layers are made of copper and, therefore, the wiring delay can be
decreased as compared with the use of aluminum, but the materials of the
conductive layers are not limited copper.

[0065]An example of the wiring structure of semiconductor devices
according to the present invention is shown in FIG. 1. In the figure,
numeral 1 denotes a semiconductor substrate made of silicon, and numeral
19 denotes an insulating layer made of silicon oxide. On the silicon
oxide insulating layer 19 is formed an insulating layer 20 having a
thickness of 0.3 μm and made of a crosslinked
poly(B-methylaminoborazine) which is a low dielectric constant material
according to the present invention. The insulating layers 19 and 20
constitute the first insulating layer.

[0066]In the insulating layer 20 is formed a first trench 3 having a width
of 0.2 μm and a depth of 0.2 μm in the pattern of a first wiring. A
first copper conductive layer 5 is filled in the trench 3. A second
insulating layer 21 having a thickness of 0.5 μm made of the
crosslinked poly(B-methylaminoborazine) is formed on the insulating layer
20 and the first copper conductive layer 5. In the second insulating
layer 21 is formed a hole 8 having a diameter of 0.15 μm and extending
to the first copper conductive layer 5, and the hole 8 is filled with
copper to form a second copper conductive layer 10 so as to contact the
first copper conductive layer 5.

[0067]On the insulating layer 21 is formed a third insulating layer 22
having a thickness of 0.2 μm made of the crosslinked
poly(B-methylaminoborazine). In the third insulating layer 22 is formed a
second trench 12 having a depth of 0.2 μm in the pattern of a second
wiring. The bottom of the trench 12 extends to the insulating layer 21,
and copper is filled in the trench 12 to form a third copper conductive
layer 13. An insulating film 23 made of the crosslinked
poly(B-methylaminoborazine) is formed on the insulating layer 22 and the
third copper conductive layer 13.

[0068]In semiconductor devices having such a structure, all copper
conductive layers, that is, the first copper conductive layer 5, the
second copper conductive layer 10 and the third copper conductive layer
13, are in contact with the insulating layers 20, 21 and 22 and film 23
made of an insulating material comprising the low dielectric constant
material of the present invention. Thus, copper diffusion from the
conductive layers can be prevented from occurring. Furthermore, since the
insulating layers 20, 21, 22 and 23 have a dielectric constant of 2.2 and
also do not require a barrier metal layer, the wiring capacitance can be
reduced as compared with conventional wiring structure shown in FIG. 6,
whereby high speed operation of semiconductor devices can be ensured.

[0069]FIG. 2 is a sectional view of a semiconductor device showing a
further embodiment of the present invention. An insulating layer 19 made
of silicon oxide is formed on a silicon semiconductor substrate 1. On the
silicon oxide insulating layer 19 is formed an insulating layer 20a
having a thickness of 0.3 μm and made of an amorphous crosslinked
poly(B-methylaminoborazine) which is a low dielectric constant material
according to the present invention. The insulating layers 19 and 20a
constitute the first insulating layer.

[0070]In the insulating layer 20a is formed a first trench 3 having a
width of 0.2 μm and a depth of 0.2 μm in the pattern of a first
wiring. A first copper conductive layer 5 is filled in the trench 3. A
second insulating layer 21b having a thickness of 0.5 μm made of a
mixture of microcrystalline and amorphous crosslinked
poly(B-methylaminoborazine) is formed on the insulating layer 20a and the
first copper conductive layer 5. In the second insulating layer 21b is
formed a hole 8 having a diameter of 0.15 μm and extending to the
first copper conductive layer 5, and the hole 8 is filled with copper to
form a second copper conductive layer 10 so as to contact the first
copper conductive layer 5.

[0071]On the insulating layer 21b is formed a third insulating layer 22a
having a thickness of 0.2 μm made of the same material as the
insulating layer 20a, namely amorphous crosslinked
poly(B-methylaminoborazine). In the third insulating layer 22a is formed
a second trench 12 having a depth of 0.2 μm in the pattern of a second
wiring. The bottom of the trench 12 extends to the insulating layer 21b,
and copper is filled in the trench 12 to form a third copper conductive
layer 13. An insulating film 23b made of the same material as the
insulating layer 21b is formed on the insulating layer 22a and the third
copper conductive layer 13.

[0072]In semiconductor devices having such a structure, all copper
conductive layers, that is, the first copper conductive layer 5, the
second copper conductive layer 10 and the third copper conductive layer
13, are in contact with the insulating layers 20, 21 and 22 and film 23
made of an insulating material comprising the low dielectric constant
material of the present invention. Thus, copper diffusion from the
conductive layers can be prevented from occurring. Furthermore, since the
insulating layers 20, 21, 22 and 23 have a dielectric constant of 2.3 and
also do not require a barrier metal layer, the wiring capacitance can be
reduced as compared with conventional wiring structure shown in FIG. 6,
whereby high speed operation of semiconductor devices can be ensured.

[0073]FIG. 3 is a sectional view of a semiconductor device showing another
embodiment of the present invention. An insulating layer 19 made of
silicon oxide is formed on a silicon semiconductor substrate 1. On the
silicon oxide insulating layer 19 is formed an insulating layer 25 having
a thickness of 0.2 μm and made of a poly(aryl ether). The insulating
layers 19 and 25 constitute the first insulating layer. In the insulating
layer 25 is formed a first trench 3 having a width of 0.2 μm and a
depth of 0.2 μm in the pattern of a first wiring. A first copper
conductive layer 5 is filled in the trench 3.

[0074]A first conductive film (barrier metal film) 4 having a diffusion
preventive function is formed so as to cover the surface of the trench 3.
The barrier metal film 4 is made of tantalum nitride and has a thickness
within the range of 10 to 20 nm. Copper is filled in the trench 3 covered
with the barrier metal film 4 to form a first copper conductive layer 5.

[0075]A second insulating layer 21b having a thickness of 0.5 μm made
of a mixture of microcrystalline and amorphous crosslinked
poly(B-methylaminoborazine), which is the low dielectric constant
material of the present invention, is formed on the insulating layer 25
and the first copper conductive layer 5. In the second insulating layer
21b is formed a hole 8 having a diameter of 0.15 μm and extending to
the first copper conductive layer 5, and the hole 8 is filled with copper
to form a second copper conductive layer 10 so as to contact the first
copper conductive layer 5.

[0076]On the insulating layer 21b is formed a third insulating layer 27
made of the same material as that of the insulating layer 25, i.e.,
poly(aryl ether), and having a thickness of 0.2 μm. In the third
insulating layer 27 is formed a second trench 12 having a depth of 0.2
μm in the pattern of a second wiring. The bottom of the trench 12
extends to the insulating layer 21b. A second conductive film (barrier
metal film) 11 having a diffusion preventive function against copper is
formed so as to cover the inner surface of the trench 12. The barrier
metal film 11 has the same composition and the same thickness as those of
the barrier metal film 4. Copper is filled in the trench 12 covered with
the barrier metal film 11 to form a third copper conductive layer 13. An
insulating film 23b made of the same material as the insulating layer 21b
is formed on the insulating layer 27 and the third copper conductive
layer 13.

[0077]In semiconductor devices having such a structure, the first copper
conductive layer 5 is in contact with the barrier metal film 4 and the
insulating layer 21b, and the third copper layer 13 is in contact with
the barrier metal film 11 and the insulating layer 23b. Further, the
second copper conductive layer 10 is in contact with the barrier metal 11
and the insulating layer 21b. Because of having such a structure,
diffusion of copper from the conductive layers can be prevented.
Moreover, since the insulating layers 25 and 27 made of poly(aryl ether)
have a dielectric constant of 2.8 and the insulating layers 21b and 23b
made of crosslinked poly(B-methylaminoborazine) have a dielectric
constant of 2.2, the wiring capacitance can be reduced to a level lower
than that achieved by a conventional wiring structure shown in FIG. 6,
whereby a high speed operation of semiconductor devices is made possible.
Further, since the insulating layers 25 and 27 are made of poly(aryl
ether) and the insulating layers 21b and 23b are made of crosslinked
poly(B-methylaminoborazine), the etching selective ratio is high and
accordingly it is possible to form wiring having a good shape.

[0078]In this embodiment, the layer in which second copper conductive
layer 10 is provided, i.e., insulating layer 21b, is formed from a
crosslinked poly(B-methylaminoborazine). Substantially the same effect
can be obtained also when the layer provided with the first or third
copper conductive layer 5 or 13, i.e., insulating layer 25 or 27, is
formed from the crosslinked poly(B-methylaminoborazine).

[0079]Another example of the wiring structure of semiconductor devices
using the low dielectric constant material of the present invention as an
insulating film or layer is shown in FIG. 4. A first insulating layer 29
made of silicon oxide is formed on a silicon semiconductor substrate 1.
In the insulating layer 29 is formed a trench 3 having a width of 0.2
μm and a depth of 0.2 μm in the pattern of a first wiring. A first
conductive film (barrier metal film) 4 having a diffusion preventive
function is formed so as to cover the surface of the trench 3. The
barrier metal film 4 is made of tantalum nitride and has a thickness
within the range of 10 to 20 nm. Copper is filled in the trench 3 covered
with the barrier metal film 4 to form a first copper conductive layer 5.

[0080]An insulating layer 30b having a thickness of 0.05 μm made of a
mixture of microcrystalline and amorphous crosslinked
poly(B-methylaminoborazine), in other words, microcrystals-containing
amorphous crosslinked poly(B-methylaminoborazine), which is the low
dielectric constant material of the present invention, is formed on the
insulating layer 29 and the first copper conductive layer 5.

[0081]On the insulating layer 30b is formed a second insulating layer 31
made of silicon oxide. In the second insulating layer 31 are formed a
hole 8 having a diameter of 0.15 μm and a trench 12 having a depth of
0.2 μm and a second wiring pattern. The hole 8 extends from the first
conductive layer 5 to the trench 12 formed in the surface region of the
insulating layer 31 through the insulating layer 30b and the insulating
layer 31. Second and third conductive films (barrier metal films) 9 and
11 made of tantalum nitride having a diffusion preventive function are
formed so as to cover the surfaces of the hole 8 and the trench 12.
Copper is filled in the hole 8 and the trench 12 to form second copper
conductive layer 10 and third copper conductive layer 13, respectively.
The barrier metal film is also formed at the interface between the first
copper conductive layer 5 and the second copper conductive layer.

[0082]An insulating film 23b made of the same material as the insulating
layer 30b is formed on the insulating layer 31 and the third copper
conductive layer 13.

[0083]In semiconductor devices having such a structure, the first, second
and third copper conductive layers 5, 10 and 13 are in contact with the
barrier metal films 4, 9 and 11 and the insulating layers 23b and 30b.
Thus, diffusion of copper from the conductive layers 5, 10 and 13 can be
prevented. Moreover, since the insulating layers 23b and 30b have a
dielectric constant of 2.2 and the insulating layers 29 and 31 have a
dielectric constant of 4.2, the wiring capacitance can be reduced to a
level lower than that achieved by a conventional wiring structure shown
in FIG. 6, whereby a high speed operation of semiconductor devices is
made possible.

[0084]The present invention is more specifically described and explained
by means of the following examples.

[0086]Tetraglyme was used as a solvent, and B-trimethylborazine was heated
in an Ar gas at 220° C. for two weeks with stirring and degassing
to give a highly viscous liquid. The liquid was evaporated to give a
white powder of a low dielectric constant material according to the
present invention.

[0087]This material had a chemical structure shown by the following
formula (117):

##STR00017##

and had an average molecular weight (Mn) of about 7,500.

[0088]The obtained low dielectric constant material was dissolved in
acetone and coated by spin coating method onto a quartz plate on which
gold was deposited to form a counter electrode. The coated film was then
dried at 100° C. for 10 minutes and heated at 400° C. for
10 minutes to give an insulating film according to the present invention.
The thus heat-treated film was made of a partially crosslinked
poly(B-methylboradine). Gold was deposited onto the obtained insulating
film as a main electrode.

EXAMPLE 2

[0089]Synthesis of soluble poly(B-triethylborzilene) was carried out in
the same manner as Example 1.

[0090]Tetraglyme was used as a solvent, and B-triethylborazine was heated
in an Ar gas at 220° C. for two weeks with stirring and degassing
to give a highly viscous liquid. The liquid was evaporated to give a
white powder of a low dielectric constant material according to the
present invention.

[0091]This material had a chemical structure shown by the following
formula (118):

##STR00018##

and had an average molecular weight (Mn) of about 5,500.

[0092]An insulating film was formed from the obtained low dielectric
constant material by conducting the spin coating in the same manner as in
Example 1 and drying at 100° C. for 10 minutes. Gold was then
deposited onto the insulating film as a main electrode.

EXAMPLE 3

[0093]A white powder of poly(methylborazinylamine) was prepared according
to Narula et al's method disclosed in C. K. Narula, R. Schaeffer, R. T.
Paine, A. K. Datye and W. F. Hammetter, J. Am. Chem. Soc., Vol. 109, p
5556 (1987). The thus obtained low dielectric constant material was
dispersed into acetone, and the dispersion was coated by spin coating and
dried at 100° C. for 10 minutes in the same manner as in Example 1
to give an insulating film. Gold was then deposited thereon as a main
electrode.

EXAMPLE 4

[0094]A white powder of poly(B-methylaminoborazine) was prepared according
to Kimura et al's method disclosed in Y. Kimura et al., Composites
Science and Technology, Vol. 51, p 173 (1994). The thus obtained low
dielectric constant material was dispersed into acetone, and the
dispersion was coated by spin coating and dried at 100° C. for 10
minutes in the same manner as in Example 1 to give an insulating film.
Gold was then deposited thereon as a main electrode.

[0095]Dielectric constants of the insulating films obtained in Examples 1
to 4 were measured at 25° C. and 1 MHz by using an impedance
analyzer (model 4191A made by Hewlett Packard). In order to evaluate the
water resistance, the dielectric constant was also measured with the
lapse of time.

[0096]The results are shown in Table 1.

COMPARATIVE EXAMPLE

[0097]An insulating film was formed from polyboradilene in the same manner
as in Example 1, and the dielectric constant thereof was measured. The
result is shown in Table 1.

[0098]The insulating films obtained in Examples 1 to 4 have a dielectric
constant of at most 2.4. From these results, it is understood that a
substrate having a low dielectric constant can be obtained.

[0099]Also, these polymeric borazine compounds can be graphitized by
heating at a temperature of 1,000 to 1,200° C. (Application View
of Inorganic Polymer, p 70, 1990, supervised by Naruyuki Kajiwara). Thus,
these insulating films have a thermal resistance of at least 450°
C.

[0100]Further, as apparent from the results shown in Table 1, the films
obtained in Examples 1 to 4 show no or little change in dielectric
constant with the lapse of time. Thus, it is understood that these films
have an excellent water resistance.